The present invention relates to the use of organic light emitting diodes for area illumination.
The light emitting elements in conventional bulbs (the filament of an incandescent bulb or the fluorescent material in a fluorescent bulb) are extremely bright, emit light in every direction, and are painful to view directly. Moreover, the bulb itself is not adapted to control the direction of illumination. Therefore, traditional lighting devices such as incandescent or fluorescent light bulbs typically require reflectors or diffusers to control the light output. For example, desk, table, floor and ceiling lamps conventionally use shades to diffuse and reflect light to the ceiling or floor to provide indirect lighting suitable for use in a home or office environment. These reflectors and diffusers are expensive and take considerable space.
Spotlights, track lighting, or floodlights are adapted to direct light to a preferred area but are large and relatively expensive.
Solid-state lighting devices made of light emitting diodes are increasingly useful for applications requiring robustness and long-life. For example, solid-state LEDs are found today in automotive applications. These devices are typically formed by combining multiple, small LED devices providing a point light source into a single module together with glass lenses suitably designed to control the light as is desired for a particular application (see, for example W099/57945, published Nov. 11, 1999). These multiple devices are expensive and complex to manufacture and integrate into single area illumination devices. Moreover, LED devices provide point sources of light, a plurality of which are employed for area illumination.
Organic light emitting diodes (OLEDs) are manufactured by depositing organic semiconductor materials between electrodes on a substrate. This process enables the creation of light sources having extended surface area on a single substrate. The prior art describes the use of electro-luminescent materials as adjuncts to conventional lighting (for example U.S. Pat. No. 6,168,282, issued Jan. 2, 2001 to Chien). In this case, because of the limited light output from the electro-luminescent material, it is not useful for primary lighting.
EP1120838A2, published Aug. 1, 2001 describes a method for mounting multiple organic light emitting devices on a mounting substrate to create a light source. However, this approach of mounting multiple light sources on a substrate increases the complexity and hence the manufacturing costs of the area illumination light source.
There is a need therefore for an improved OLED lighting apparatus for area illumination having a simple construction that provides a robust light but does not require additional reflectors or diffusers.
The need is met by providing a lighting apparatus that includes a solid-state area illumination light source having: a planar substrate, an organic light emitting diode (OLED) layer deposited on the planar substrate, the organic light emitting diode layer including first and second electrodes for providing electrical power to the OLED layer, an encapsulating cover covering the OLED layer, and first and second conductors electrically connected to the first and second electrodes, and extending beyond the encapsulating cover for making electrical contact to the first and second electrodes by an external power source; and a lighting fixture for removably receiving and holding the solid-state light area illumination light source in a horizontal plane, the lighting fixture including contacts for providing electrical contact between said first and second conductors and an external power source.
The present invention has the advantage of providing an inexpensive, long lived, highly efficient, light source that provides diffuse and indirect illumination without the need for additional components.